METHOD:

We examined implicit emotional face perception in soldiers with (n = 20) and without (n = 25) PTSD using magnetoencephalography to define spatiotemporal network interactions, and a subsequent region-of-interest analysis to characterize the network role of the right amygdala and medial prefrontal cortex in threatening face perception.

RESULTS:

Contrasts of network interactions revealed the PTSD group were hyperconnected compared to controls in the phase-locking response in the 2-24 Hz range for angry faces, but not for happy faces when contrasting groups. Hyperconnectivity in PTSD was greatest in the posterior cingulate, right ventromedial prefrontal cortex, right parietal regions and the right temporal pole, as well as the right amygdala. Graph measures of right amygdala and medial prefrontal connectivity revealed increases in node strength and clustering in PTSD, but not inter-node connectivity. Additionally, these measures were found to correlate with anxiety and depression.

CONCLUSIONS:

In line with prior studies, amygdala hyperconnectivity was observed in PTSD in relation to threatening faces, but the medial prefrontal cortex also displayed enhanced connectivity in our network-based approach. Overall, these results support preferential neurophysiological encoding of threat-related facial expressions in those with PTSD.

Experimental schematic and catch-trial reaction times. (A) During the implicit emotional face processing task, participants were instructed to ignore the faces and attend to the colour of the frame surrounding the face. In this example, a purple border signifies a passive viewing trial, and the blue border signifies a catch trial, for which responses were to made as fast as possible. (B) Reaction time for correct hits on catch trials. No significant main effects or interactions were observed, although there was a slight trend for faster responses in the control group, especially when presented with happy faces.

Time-frequency spectrograms of phase-locking values for implicit face processing trials for PTSD (left column) and control soldiers (right column), in the angry (top row) and happy (bottom row) conditions. PLV values during the ‘Baseline’ period (denoted by the B, -100 to 0 ms) were subtracted from the ‘Active’ window (0 to 900 ms). Warm colours indicate an increase in phase locking relative to baseline, or ‘ongoing’, phase synchrony. Both groups showed stimulus-dependent (presented at 0 ms) increases in inter-regional phase locking that peak around 175 ms, evident when viewing both types of emotional faces, although these phase-locking responses are particularly pronounced in the PTSD group.

Group difference (PTSD minus control) spectrograms (left) and functional connectivity contrasts (right). Time-frequency representations for PTSD minus control in the angry (top) and happy (bottom) trials show relatively enhanced 2–24 Hz increase in PLV for PTSD in the 100–200 ms time window, more prominent for angry faces. Connectivity analysis of temporally- and frequency-averaged adjacency matrices revealed significant increases in PLV in the PTSD group compared to controls for angry (t > 3, pcorr < 0.05), but not happy (pcorr > 0.05), facial expressions. These elevated interactions were particularly evident for connections involving the posterior cingulate, and the right medial frontal orbital cortex. The node radius denotes the strength of the connections for the vertices, whilst the connection width and colour warmth (yellow is greater, red is less) signifies the edge weight between regions.

Region-of-interest graph analysis of right amygdala and medial prefrontal cortex seeds for the viewing of angry faces, in PTSD (blue bars) and controls (grey bars), as well as the degree of oscillatory synchronisation between those two regions. Values are baseline-corrected against the pre-stimulus window. Significant differences denoted by *p < 0.05.